Cold hardiness & minimum temperature

Is Tree Germander (Teucrium fruticans)cold hardy? Hardiness zone & min temp

Also called Tree germander, Shrubby germander, Silver germander.

More about tree germander

About Tree Germander

Teucrium fruticans · also called Tree germander, Shrubby germander · herb

Teucrium fruticans is an evergreen, silver-leaved shrub native to the western Mediterranean — Portugal, Spain, southern France, and North Africa — where it colonises dry rocky slopes and garrigue. Its stems and undersides of leaves are densely white-felted, giving a striking year-round silver effect, while two-lipped pale lavender-blue flowers appear from spring through summer. The most important care fact is that it cannot tolerate prolonged freezing temperatures or waterlogged soil, so in colder gardens it must be given wall protection or overwintered under glass. Teucrium fruticans contains diterpenoids and should be treated as mildly toxic to pets.

Cold limit: USDA 8-11 · RHS H3 (-5 to 35°C)

Watch for — Frost damage to stems: Hard frosts below -5°C kill young growth and can cut the plant back to the ground; prune out dead wood in spring and protect with fleece in exposed positions or against a warm south-facing wall.

What tree germander's hardiness rating actually means

Tree Germander is half-hardy (RHS H3). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Its RHS rating of H3 means: Half-hardy — comes through mild UK winters outside but is killed by a hard freeze. On the US scale that maps to USDA 8-11 — the zones where it can be left outdoors year-round.

New to these scales? The USDA hardiness zone map explained covers how the zone numbers work, and you can find your own zone with the zone finder.

Minimum temperature — and what happens below it

Minimum survivable temperature is roughly about −5 to 1 °C — a light, short frost only. Tree Germander shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for tree germander as it gets too cold:

Down to roughly about −5 to 1 °C it copes, especially if dry and sheltered.
A sustained hard frost collapses the top growth; whether it returns depends on whether the roots, crown or tubers froze.
Wet cold is far more lethal than dry cold for this plant — soggy, frozen soil is the usual killer.

Can tree germander go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-11 or a frost-free UK microclimate.
In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter.
A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

Work back from your local frost dates with the frost-date calculator: the last spring frost and first autumn frost are what really decide when tree germander can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H3 figure above.

Frost protection for borderline tree germander

Tree Germander is right on a hardiness edge in many gardens, so if you are pushing it, these measures buy it the margin it needs:

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost.
Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse.
Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones.
Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.

Tree Germander hardiness — frequently asked questions

Is tree germander cold hardy?

Tree Germander is half-hardy (RHS H3). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Borderline outdoors. In its mild end of USDA 8-11 (and sheltered UK gardens) tree germander can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature tree germander can survive?

Minimum survivable temperature is roughly about −5 to 1 °C — a light, short frost only. Tree Germander shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is tree germander?

Tree Germander is rated USDA 8-11 and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can tree germander survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-11 or a frost-free UK microclimate. In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter. A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

How do I protect tree germander from frost?

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost. Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse. Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones. Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.